WIP — Start on 1.9 support

Very much a rough WIP, just took a fast crack at adding 1.9 support. Rebased initial bits. Got most of the event API changes covered (e.g, `rb_event_t` -> `rb_event_flag_t;`). Naturally all still works for 1.8.7.

`ruby_frame` doesn't seem available on 1.9; looks like we can do something with `GET_THREAD()`

cc @tmm1, please feel free to add shit to this at will